PROJECT SUMMARY Although postural instability is one of the most common and devastating complaints after concussion, there are currently no sensitive, objective or easy measurements for this complex problem involving multiple components of the central nervous system. Therefore, objective measures of postural control are not commonly used in clinical decision-making. Our long-term goal is to improve the management and rehabilitation of concussion, through improved quantification of balance impairment in athletes. The objective of this proposal is to use inertial sensors to quantify and determine patterns of recovery for both static and dynamic balance after an injury to the brain, and to determine the most sensitive metrics to help identify those who do not recover in the expected 5-day window. Aim 1.To longitudinally characterize postural sway in college athletes after a concussion. We hypothesize that a subset of participants who sustain a concussion will have a measurable and significant increase in postural sway immediately post-injury and this abnormal postural control will persist for more than one week. Aim 2. To determine the most sensitive gait metrics after concussion. We hypothesize that adding challenging gait conditions (fast walking, head turns and secondary task) to the instrumented 2 minute walk test will increase the sensitivity and specificity of post- concussion assessment. To assess recovery of static and dynamic balance, 25 athletes post-concussion will be followed for 8 weeks after injury (tested twice in the first week after injury and then weekly for 7 more weeks, for a total of 9 study visits). Healthy control participants will be tested along the same time-points for comparison. Inertial sensors will provide data on postural sway and gait variability as primary outcome measures. These proposed studies have the potential to change the way in which athletes are monitored post- concussion and move the field in a much-needed, objective direction. Until now, there has not been both a practical and objective measure of postural control deficit after concussion and we believe that a subset of athletes are returning to play before they have optimal control of their complex balance system, further predisposing them to a second detrimental concussion. If we can identify people who have not recovered in this, often overlooked, domain we could more confidently advise rest, rehabilitation, or return to play when appropriate. Furthermore, this technique could be used in other high-risk populations, including Veterans and younger children who suffer head trauma. This is the first study to apply promising, new inertial sensor technology to determine how a concussion affects static and dynamic postural control.